You 100% can fix this. Feather in new wood if you dont have any extra and then sand and finish.

Ideally you should refinish everything or at least that room. But you could try and sand and finish the repair spot. Only problem is matching the color. A pro can get damn close but no one even pros can get it perfect. Hence why i suggest refinishing the entire room

Thanks Greg!
We are planning on refinishing all of the hardwood, but like you said, the problem is the color. We have a piece of unfinished oak and a few stains we've narrowed it down to. As long as its close that would be great, because we will be using a rug in the room anyway.
Now we just have to remove the old planks carefully so we can reuse them with the new wood we have to purchase.

I have an old house with old white oak floors. When I pulled up carpeting in den, I discovered it wasn't wood plank but cheap plyboard or something. Kitchen had some sort of tile over linoleum. I had a contractor cut out existing floor in den and kitchen (I'm on a pier & beam, so I have a wood subfloor, which the contractor left intact). He installed new white oak, and did a good job matching up the lines in adjoining hall.

So I then have amber colored old white oak floors and then the new white oak unfinished floors. Several wood floor refinishers have assured me they can refinish the old floors and the new flooring and match them with the same stain. There may be SOME slight difference, but not much, if any. That's good enough for me. Expensive, but the old floors need to be refinished, anyway. They all said they do this on occasion. They just sand the old floors down to the raw wood.

As for a damaged area, contractors told me it's no problem to pull out what they consider a damaged area and feather in new white oak strips. I'm not having that done because I think the refinishing will deal with the discoloration, and I don't want to get into pulling up any more existing flooring.

Some slight difference is good enough for us too. Looks like we are going to try to feather in new wood and refinish the floors all at once (living and dining room share the same flooring). That is IF we can pull up the existing planks without damaging them. Worst case scenario, the whole section of hardwood needs to be changed where that damage is to the opposite wall.
Thank you very much for the input bpollen!

We sanded down the floors in two houses - one kitchen didn't have wood underneath the vinyl so we had to put in new wood - which the contractor was able to match beautifully to the living room. The cottage DID have wood under the vinyl - but 100 years of glue and gunk too. They were able to sand it down and match the hallway and living room - we also went with a darker stain to camouflage some water damage in spots (most likely from potted plants directly on the wood floors bah!)

My big lesson, though, was on a spot where we expanded a doorway - I didn't think about the floor like a nooob. The contractor matched the new wood - but there is a seam around it. Maybe this is what feathering solves? A terrible moment but given all the things that went RIGHT, I just filed it in my "things learned on my first remodel" folder and kept moving....ha.

I'm with the others - totally fixable!!

Good luck with it! We used a dark walnut stain and glossy finish and love it.

I will keep the doorway in mind since we are considering a layout change with the adjoining rooms.

Thank you slowjane!